Process for post-treating hot briquettes and the like

ABSTRACT

Hot briquettes formed at temperatures in the range of 350*-550*C are conveyed through a shaft zone countercurrent to oxygencontaining gases. The oxygen-containing gases are preferably recycled through the process and admixed with air as a source of oxygen. This results in a combustion of carbon on the surface of the briquettes and of the gases and tar vapors released by the briquettes when so heated. Briquettes post-treated according to the invention have an optimum crushing strength and abrasion resistance making them easily transportable and useful in blast furnaces.

United States Patent Schmalfeld et al.

[ PROCESS FOR POST-TREATING HOT BRIQUETTES AND THE LIKE [75] Inventors:Paul Schmalfeld, Bad Homburg;

Helmu. Hahn, Hunau; Joachim Lehmann, Essen-Haarzopf; Kurt Kleisa,Essen-Frintrop, all of Germany [73] Assignee: MetallgesellschaftAktiengesellschaft,

Frankfurt am Main Germany [22] Filed: Aug. 16, 1973 [21] Appl. No:389,052

[30] Foreign Application Priority Data Sept, 16. I972 Germany 2247l0l{52} US. Cl. 44/10 K; 44/l0 H [51] Int. Cl. ClOL 5/00 [58] Field ofSearch 44/l0 K 10 R, l R. 10 H, 44/ 10 J [56] References Cited UNITEDSTATES PATENTS 1357396 12/]967 Gusior et a] 44/] R NOV. 11,1975

3.384557 5/l968 Saller 44/) R 3.663J86 5/1972 Dzhaparidze et al.. 44/10H 3.67%449 7/1973 Schmalfeld et al, H 44/IU R Primal)- E.\'anlilwrCarlF. Dees Attorney, Agent. or Firm-Dinklage, Dinklage 84 Sprung [57]ABSTRACT Hot briquettes formed at temperatures in the range of 3S0550Care conveyed through a shaft zone countercurrent to oxygencontaininggases, The oxygencontaining gases are preferably recycled through theprocess and admixed with air as a source of oxygen. This results in acombustion of carbon on the surface of the briquettes and of the gasesand tar vapors released by the briquettes when so heated. Briquettcspost-treated according to the invention have an optimum crushingstrength and abrasion resistance making them easily transportable anduseful in blast furnaces.

6 Claims. 1 Drawing Figure US. Patent Nov. 11, 1975 PROCESS FORPOST-TREATING HOT BRIQUETTES AND THE LIKE BACKGROUND This inventionrelates to a process of aftertreating hot briquettes or similar shapedbodies which contain caking coal and have been made at a temperaturebetween about 350 and 550C.

Hot briquettes are preferably made by pressing a mixture of caking coaland non-softening solids, partic ularly fine-grained coke, attemperatures in the plastic region of the caking coal. The coke isheated to such a temperature that the mixture of coke and predried andpossibly preheated caking coal has a mixed temperature in the range of400 550C. and at this temperature is fed to a briquetting press. Theratio of coke to caking coal varies widely in dependence on the natureand the caking capacity of the coal which is used and above all on theporosity and also the strength of the hot coke. Conventional ratios are60-75% coke to 40-25% caking coal by weight. The temperature of themixture is preferably kept within the range of 4405 20C., particularlybetween 450 and 480C.

SUMMARY It is an object of the invention to provide a process to makebriquettes which have an optimum crushing strength and abrasionresistance and which are highly suitable for being transported, handledbefore the blast furnace and used as a reducing agent in the blastfurnace. This is accomplished according to the invention by conveyinghot briquettes through a shaft zone, countercurrent to oxygen-containinggases. In this operation, the presence of these gases, which preferablycontain admixed air, results in a combustion of carbon on the surface ofthe briquettes and of the gases and tar vapors released by thebriquettes when heated. To heat the briquettes by, e.g., lC., about l.2%of the carbon of the hot briquettes or an equivalent amount of volatileconstituents must be burnt. The combustion on the surface of the hotbriquettes may be suppressed to a high degree by an addition ofcombustible gases unless this effect is produced by the volatileconstituents which have been released from the briquettes.

DESCRIPTION OF THE DRAWING The present invention will be more fullyunderstood from the following description taken in conjunction with theaccompanying drawing which is a schematic flow diagram of apparatussuitable for carrying out the process of the invention.

DESCRIPTION The combustion in the shaft is controlled in such a mannerthat the hot briquettes are heated to a certain temperature which is50200C., preferably about 100C., above the briquetting temperature. As aresult, substantially all of the residual tar contained in the hotbriquettes is removed and their content of volatile con stituents isreduced to or below 5% by weight. The briquettes having this compositionnow posses the desired crushing strength and abrasion resistance.

An essential feature of the invention resides in admixing air at acontrolled rate to gases which are recirculated through the shaft zone.As soon as the ignition temperature has been reached and the combustiontemperature is sufficient to effect a higher temperature rise of therecirculated gases and of the hot briquettes, this air causes thecombustion of the recirculated gases which flow through the briquettecharge in the shaft zone and are subjected to a temperature rise. Theair is added to the recirculated gases at such a rate that thecombustion on the surface of the hot briquettes or of the combustiblecomponents of the recirculated gases just results in the desiredtemperature. It will be desirable to admix the air to the recirculatedgases before they enter the briquette charge. Alternatively, the air maybe added through distributing means in the top half of the briquettecharge where the recirculated gases and briquettes are at a highertemperature.

An example of the process according to the invention will now beexplained with reference to the drawing:

The hot mixture of coke and caking coal is pressed in a doubleroll pressI to form hot briquettes. The temperature of the mixture is in the rangeof 4005 50C., preferably between 450 and 480C. From the briquettingpress l, the briquettes move by a horizontal conveyor 2 and a steepconveyor 3 to a feed chute 4, which delivers them into shaft zone 5. Thechute 4 is suitably provided with a grate or screen 6 for a removal offines abraded from the briquettes and any undersize particles.

Under the action of gravity, the briquettes move through the shaft zone5 as a closed charge continuously from top to bottom. The valve member 8associated with the shaft is controlled so that the shaft is alwaysentirely filled with briquettes up to the distributing chutes 7.

At the lower end of the shaft 5, recirculated gases at a low temperatureare fed into the shaft 5 through a conduit 9. These gases will bereferred to hereinafter as recirculated gases. The recirculated gasesconsist normally of the exhaust gases which have been formed as a resultof the addition of air and the combustion and which still containoxygen. Water vapor from the means for the direct-contact cooling of therecirculated gases with water or from the means for the final cooling ofthe hot briquettes may be admixed to the recirculated gases. Air flowingthrough the conduit 10 at a metered rate is admixed to the recirculatedgases when they are at a temperature between 30 and 200C. before theyenter the shaft 5 via conduit 9.

In the shaft zone 5, the mixture of recirculated gas and air flows frombottom to top through the hot briquette charge so that the latter iscooled in the lower portion 5a of the shaft while the countercurentlyflowing gases are heated. In In the upper portion 5b of the shaft, theignition temperature is reached and the air in the recirculated gasessupports the combustion of carbon on the surface of the hot briquettesand the combustion of the gases and tar vapors which are released fromthe briquettes as they were heated.

The air is added to the recirculated gases at such a rate that thecombustion results just in the desired temperature at the hotbriquettes. When briquetted at a temperature of, e.g., 450C, the hotbriquettes may cool to, e.g., 420C. until they enter the shaft zone 5and are then heated in the shaft to about 500C. by the partialcombustion in the charge. The temperature may be increased to 550600 ormore if combustion air is added at a suitable rate. It is important toheat the briquettes to such an adjusted temperature that virtually allresidual tar in the hot briquettes is eliminated and their content ofvolatile constituents is reduced below 5% by weight.

Owing to the relatively low 0, content of the recirculated gases and thelow combustion temperatures, the combustion is slow and takes place inan extended zone (5b) of the briquette charge. The recirculated gaseswhich leave the shaft 5 at the upper end thereof always contain still acertain amount of unconsumed oxygen. A number ofthermocouples (notshown) which are distributed in the shaft zone 5 over the height of thebriquette charge and serve to monitor the cooling, combustion andtemperature rise of the briquettes. The temperature of the recirculatedgases emerging from the briquettes charge also furnishes an indicationof the temperature to which the hot briquettes have been heated.

The residence time of the hot briquettes which descend in the shaft 5 isgenerally -20 minutes in the heating zone 5b and about 20-40 minutes inthe cooling zone 5a. In the case of a high temperature in the heatingzone 5 b, a short residence time will be suffcient. The success of theprocess is desirably checked by a determination of the contents ofresidual tar and volatile constituents in the treated hot briquettes.The air rate may be controlled to ensure a suitable combus tion and aheating of the hot briquettes to the desired temperature in the top partof the briquette charge.

The recirculated gases which emerge from the briquette charge at the topend of the shaft zone 5 are fed by a conduit 11 into a cyclone zone 12,where the dust which has been entrained from the briquette charge isremoved. The gases are then cooled in a cooler 13 to a temperaturebetween 30 and 200C The cooler may be a waste heat boiler for thegeneration of steam, a water-evaporating spray cooler, or an indirectlycooled cooler using air or water. The cooled recirculated gases and theadmixed air are returned into the shaft 5 by a blower 14. Any surplusrecirculated gas is withdrawn at 16.

The hot briquettes discharged from the shaft 5 at its discharge end 15may be postcooled quickly to avoid selfignition, which might otherwisebe possible. This postcooling may be accomplished in various ways, e.g.,by an aftertreatment with water, which may be sprayed or may becontained in dip basins, or by a mere air cooling.

In the process described hereinbefore, the air conducted in the conduit10 is admixed to the recirculated gases before they enter the briquettecharge in the shaft 5. In an alternative process, the air may be addedthrough distributing means in the top half of the shaft 5. Thedistributing means consist, e.g., of a multiplicity of parallelhorizontal tubes having uniformly spaced air outlet openings.

The air is fed to the tubes 20 through a supply conduit manifold 22. Thedistributing tubes 20 may be disposed under downwardly open rooflikeelements 21, which serve to stiffen the tubes 20 and also simultaneouslyto premix the air with the recirculated gases. This may be accomplishedin the space under the roofs 21 outside the briquette charge. Thesedistributing members may be used to provide over the height of the shafta temperature profile which differs somewhat from that obtained when airis supplied through conduit 10. The supply of air through thedistributing tubes 20 may be combined with the admixing of air throughthe conduit 10.

If the recirculated gases which emerge from the briquette charge throughthe conduit 11 still contain unburnt or undecomposed tar vapors whichmay form undesired deposits in the cyclone or cooler it will be suitableto admix air at a controlled rate to the recirculated gases before orafter the cyclone in order to cause the combustion of these tar vaporsand of any permanent gases which are still present. If this combustionis not sufficiently intense because the temperatures are too low, itwill be suitable to admix not only air but to admix hot combustion gasesand an excess of air so that the recirculated gases are sufficientlyheated.

The process is applicable not only to hot briquettes which have beenmade at a temperature of 400550C. from a mixture of fine-grained cokeand caking fine coal, but also to hot briquettes which have been made bypressing from coal or a coal mixture which has been heated to atemperature between 350450C. whereas hot coke has not been added. Theprocess is also applicable to the aftertreatment of hot pellets whichhave been made in a rotary drum from a mixture of hot, fine-grained cokewith predried or preheated, caking fine coal with or without an additionof tar pitch.

We claim:

1. Process for post-treating hot briquettes or similar shaped bodiescontaining caking coal which have been made at temperatures betweenabout 350 and 550C, which comprises conveying the hot briquettes througha shaft zone countercurrent to oxygen-containing gases, thereby raisingthe temperature of said briquettes to from 50-200C above said shapingtemperature by combustion within said shaft zone of carbon of thebriquettes and of gases and tar released by the briquettes when soheated.

2. Process of claim 1 wherein air is admixed at a controlled rate tosaid gases which are recirculated through the shaft zone.

3. Process of claim 2 wherein the air is admixed before the recirculatedgases enter the briquettes in the shaft zone.

4. Process of claim 2 wherein the air is admixed by distributing meansarranged in the top half of the briquettes in the shaft zone.

5. Process of claim 4 wherein the air is added at such a rate that thecombustion of combustible constituents of the recirculated gases and apartial combustion of the hot briquettes at their surface result in aheating of the hot briquettes to a temperature which exceeds thebriquetting temperature by about C.

6. Process of claim 1 wherein air is admixed to recirculated gases whenthey have left the shaft zone and/or when subjected to dust collectionin a cyclone zone following the shaft zone, and said admixed air resultsin a substantial combustion or decomposition of tar vapors entrained inthe recirculated gases.

* k r w

1. PROCESS FOR POST-TREATING HOT BRIQUETTE OR SIMILAR SHAPED BODIESCONTAINING CAKING COAL WHICH HAVE BEEN MADE AT TEMPERATURES BETWEENABOUT 350* AND 550*C., WHICH COMPRISES CONVEYING THE HOT BRIQUETTESTHROUGH A SHAFT ZONE CONTERCURRENT TO A OXYGEN-CONTAINING GASES, THEREBYRAISING THE TEMPERATURE OF SAID BRIQUETTES TO FROM 50$-200$C ABOVE SAIDSHAPING TEMPERATURE BY COMBUSTION WITHIN SAID SHAFT ZONE OF CARBON OFTHE BRIQUETTES AND OF GASES TAR RELEASED BY THE BRIQUETTES WHEN SOHEATED.
 2. Process of claim 1 wherein air is admixed at a controlledrate to said gases which are recirculated through the shaft zone. 3.Process of claim 2 wherein the air is admixed before the recirculatedgases enter the briquettes in the shaft zone.
 4. Process of claim 2wherein the air is admixed by distributing means arranged in the tophalf of the briquettes in the shaft zone.
 5. Process of claim 4 whereinthe air is added at such a rate that the combustion of combustibleconstituents of the recirculated gases and a partial combustion of thehot briquettes at their surface result in a heating of the hotbriquettes to a temperature which exceeds the briquetting temperature byabout 100*C.
 6. Process of claim 1 wherein air is admixed torecirculated gases when they have left the shaft zone and/or whensubjected to dust collection in a cyclone zone following the shaft zone,and said admixed air results in a substantial combustion ordecomposition of tar vapors entrained in the recirculated gases.